Crypto-Christianity is the secret practice of Christianity, usually while attempting to camouflage it as another faith or observing the rituals of another religion publicly. In places and time periods where Christians were persecuted or Christianity was outlawed, instances of crypto-Christianity have surfaced.

During the initial development of the Christian Church under the Roman Empire followers often had to practice in secret.[citation needed] Official policy under Trajan was to provide Christians with the choice between recanting and execution.[1] The term crypto-Christianity can be applied to that segment of the church population which concealed its Christian beliefs as a means to avoid persecution. In contrast, many Christians, including Polycarp,[2] chose to retain their beliefs and suffer persecution, due to the fact that Christian doctrine forbade public profession of another religion even while holding a mental reservation against it, which made it stricter than Muslim (taqiyya) or Jewish opinions on the manner, but many did so out of weakness:

All the inhabitants of the empire were required to sacrifice before the magistrates of their community 'for the safety of the empire' by a certain day (the date would vary from place to place and the order may have been that the sacrifice had to be completed within a specified period after a community received the edict). When they sacrificed they would obtain a certificate (libellus) recording the fact that they had complied with the order.[3]

Christianity was introduced to Japan during its feudal era by Saint Francis Xavier in 1550. From the beginning, Christianity was seen as a threat to the power of the shōgun. In 1643, Christianity was banned, all churches were destroyed, all known Christians tortured and demanded to convert to Buddhism or face execution, and all signs of Christian influence were systematically eliminated. The ban was not lifted until 1858.

During this period, faithful converts moved underground into a crypto-Christian group called kakure Kirishitan or "hidden Christians". Crypto-Christian crosses and graves, cleverly styled during these two centuries to resemble Buddhist imagery, can still be seen in the Shimabara Peninsula, Amakusa islands and far south in Kagoshima.

Shūsaku Endō's acclaimed novel Silence draws from the oral history of Japanese Catholic communities pertaining to the time of the suppression of the Church.

An early attestation and justification of cryptochristianism is found in an epistle of Patriarch Ioannes 14th (Ιωάννης ΙΔ')(1334-1347) of Constantinople to the Christians of Bithynia (Asia Minor). He says that "those [christians] who by the fear of punishment [by the muslims] want to believe and practice christianity secretely, they will be also saved, provided they study god's orders as far as possible".[4]

Due to the religious strife that has marked the Balkan Peninsula and Anatolia, instances of crypto-Christian behavior are reported to this day in Muslim-dominated areas of the former Yugoslavia, Albania, and Turkey.[a] With the threat of retribution for the religious and ethnic conflicts, many Christian minority groups keep their religion private to protect themselves. Crypto-Christianity was mostly practiced following the Ottoman Turkish conquests of the Balkans, but the earliest scholarly record of the phenomenon dates to 1829. Linobamvaki in Cyprus traced their ancestry to both Catholics, Maronites and Greek Orthodox Christians who converted under Ottoman oppression. The Laramans in southeastern Kosovo hailed from the northern Albania highlands and converted after settling in the 18th century.

Crypto-Greek Orthodox are reported to many parts of the Ottoman Balkans and Anatolia. A good account of the Crypto-Christians among Pontic Greeks from northeastern Anatolia and the Pontic Alps region (often referred to as Stavriotes), including bibliography on other parts of the Ottoman Empire, is given by F. W. Hasluck.[6]

Further information is in "The Crypto-Christians of the Pontos and Consul William Gifford Palgrave of Trebizond," London: Valiorum Reprints, 1988, from Peoples and Settlement in Anatolia and the Caucasus 800-1900, by Anthony Bryer

Crypto-Armenians are believed to represent at least two groups of Armenians living in modern Turkey. One has been Islamized under the threat of physical extermination particularly during Armenian pogroms in 1896 and the Armenian Genocide of 1915. Representatives of a different, much smaller crypto-Armenian group live in separate villages inhabited by Turks and Kurds in Eastern Turkey (on the territories of traditional Armenian homeland). This group differs from the above-mentioned "Islamized" type by the process and depth of Islamization.[7]

In the first few centuries the Christian religion spread rapidly around the Mediterranean region with Egypt and Syria becoming especially important centers of the religion. Even as the Roman Empire disintegrated between the 5th and 7th centuries, the Christian faith only deepened in the Eastern Mediterranean. During the 7th century the Rashidun Caliphate took over what is now called the Middle East. Initially Christianity was well tolerated though preferential treatment was given to Muslims. However, often the only actual requirement for being considered a Muslim was to profess a belief in God and proclaim Mohammed as his prophet. As a result, many Egyptians, Syrians, and others in the region officially converted to Islam while still adhering to Christian practices.

As oppression of Christians arose under the Fatimid Caliph Al-Hakim, Christian (and Jewish) practices became more hidden. Secretive communities appeared in Egypt during the 11th century and in Morocco in the 12th century under the Almohads rule. Many Crypto-Christian communities existed in Middle-East till the 19th century, as Muslim authorities continued to tolerate minimal requirements of obedience by converts. From late 19th century onward most of crypto-religious groups disappeared as a result of the rise of nationalism in the new Middle Eastern states.[8]

Many Christian communities in the Soviet sphere of influence during the Cold War had to go underground in so-called Catacomb Churches. After the break-up of the Warsaw Pact and the end of the Soviet era in the 1990s, some of these groups re-joined the official above-ground churches, but others continued their independent existence, believing the official churches had been irreconcilably tainted by their cooperation with the previous Soviet-supported regimes.

In a unique instance of crypto-Christianity occurring in a majority Christian nation, the underground Confessing Church consisted of German (Protestant) Christians who had separated from the unified Protestant Reich Church that had been created after Hitler's rise to power in 1933 and condoned fascist policies. While many of their leaders actively opposed Hitler's anti-Semitic policies, the Confessing Church's opposition was directed primarily against the state's meddling in church affairs, such as the persecution of pastors with Jewish ancestry. Many leading figures of the Confessing Church were eventually arrested and imprisoned in concentration camps, most notably Dietrich Bonhoeffer who was a co-conspirator in an unsuccessful assassination attempt on Hitler by officers of the Abwehr in 1943. Bonhoeffer was subsequently imprisoned in Flossenbürg concentration camp and eventually executed.